1. Technical Field
The present invention relates to a color cathode ray tube having a luminescent surface with color filters and a manufacturing method thereof.
2. Background Art
In general, as shown in FIG. 6, on an interior surface of a panel 13 (face panel) of a color cathode ray tube 60, a phosphor screen 61 with phosphor layers of each color of blue (B), green (G) and red (R) are formed arranged in dots or in stripes. On each of these phosphor layers, an electron beam 62 output from an electron gun 63, and deflected by a deflector 64, is impinged to emit each corresponding color, thereby resulting in the display of images. Here, a panel 13 of a color cathode ray tube 60 is constituted of a faceplate with an exterior surface formed flat and a skirt portion (sidewall portion) connected thereto.
In such a color cathode ray tube, in order to absorb light from other than phosphors to improve contrast, between adjacent phosphor dots or phosphor stripes that are pixels, a light absorption layer (black layer) is disposed as black matrix.
The light absorption layer (the black layer) is formed, for instance, in the following way. First, on an interior surface of a glass panel, photo-resist is coated, followed by exposure through a shadow mask and development, to form a resist pattern arranged in dots or stripes. Thereafter, on a resulting structure a dispersion liquid of light absorbing material (black material) such as graphite is coated to be fixed on the resulting structure. Next, the surplus black layer adhered to the interior surface of the sidewall of the panel is scraped to be removed (generally referred to as trimming), followed by decomposition of the resist layer due to a resist decomposition agent such as an aqueous solution of hydrogen peroxide. Thereby, the resist layer is dissolved and peeled off as a whole including the black material adhered thereon.
Here, scraping of the surplus black layer adhered on the interior surface of the sidewall of the panel, that is trimming, is implemented in the following two ways. In one way, as shown in FIG. 2, by use of a rotary brush 11, the black layer is scraped or rubbed mechanically, followed by water washing. In the other way, as shown in FIG. 3, the black layer is dipped in a solution of decomposition agent 12 of the black material such as an aqueous solution of ammonium fluoride to chemically decompose the black layer. Thereby, the black layer is peeled off, followed by water washing. In these figures, reference numeral 13 denotes a panel, reference numeral 13f denotes a faceplate thereof, and reference numeral 13s denotes a sidewall, respectively. In addition, reference numeral 14 denotes the black layer (black matrix) formed in a prescribed pattern on the interior surface of the faceplate 13f of the panel and 14s denotes the surplus black layer adhered on the interior surface of the sidewall 13s. 
Recently, in a color cathode ray tube, with an object to improve brightness and contrast of the luminescent surface, between the panel and phosphor layers, corresponding to each emission color of the respective phosphors, color filters (an optical filter layer) transmitting only the light of desired wavelength are disposed.
In order to form such an optical filter layer, for instance, on an interior surface of a panel thereon a black layer (black matrix) is formed and a dispersion liquid of pigment is coated to form a pigment layer, followed by coating photo-resist thereon, exposing and development. By repeating this process, pigment layers of the respective colors are patterned in dots or in stripes. In the course of formation of such an optical filter layer, surplus pigment layers (filter layers) adhered on the interior surface of the sidewall of the panel, in the identical way as the black layer, are scraped to be removed (trimming). Reference numeral 15s denotes the surplus filter layer adhered on the interior surface of the sidewall 13s of the panel.
The reason why the trimming of the surplus black layer and surplus filter layer both adhered on the interior surface of the sidewall of the panel is necessary is as follows. After the phosphor layers are formed, a funnel 65 (FIG. 6) is joined airtightly by use of frit glass or the like to the sidewall portion of a panel 13. When the black layer or filter layer remains adhered in the neighborhood of an edge surface of the panel being joined to the funnel 65, in sealing, there is an inconvenience that cracks may occur at the portion connecting with the funnel 65.
Further, in detaching the mask in the step of later patterning, the surplus black layer or the filter layer may be rubbed by a mask-frame or a frame-holder to result in peeling off in certain cases. Thereby, peeled fragments tend to clog holes of the shadow mask. In order to prevent such an inconvenience from occurring, trimming is implemented onto the surplus layer of the interior surface of the sidewall of the panel.
However, in trimming such a black layer or optical filter layer, so far no particular attention has been paid to the lengths from an edge of the panel being joined to the funnel 65 to the peeling edges of the respective surplus layers (hereinafter refers as trimming dimension). It has thereby frequently occurred that, as shown in FIG. 4, the trimming dimension (a) of the black layer 14s is shorter than the trimming dimension (b) of the filter layer 15s. 
In such cases, in trimming the filter layer 15s, the circumference portion of the surplus black layer 14s is likely to be scraped off again. Fragments of the black layer that are pulverized due to scraping by the rotary brush or fragments dissolved and peeled off due to immersion into an aqueous solution of ammonium fluoride enter into the interior surface of the faceplate 13f of the panel washing with water, and remain there without being completely removed. As a result of this, as shown in FIG. 5, a small fragment 16 of the black layer may result in a display defect. In FIG. 5, reference numeral 17 denotes an interior surface of the faceplate 13f and 18 denotes a black layer formed in a stripe as the black matrix.
Thus, the fragment 16 of the black layer entered into the interior surface 17 of the faceplate, in washing with water during trimming of the filter layer, for instance, can be removed by increasing an amount of washing water up to 20 to 30 l/min. In such a case, while the display defect due to the residual fragments of the black layer can be reduced, the filter layer is likely to be peeled off due to the water washing. Thereby, increasing the amount of washing water is difficult to put to practical use.
In trimming the black layer, the small fragments of the black layer peeled and pulverized by the rotary brush or dissolved and peeled in an aqueous solution of ammonium fluoride may come into the interior surface of the panel in washing with water. In such cases, since the small fragments of the black layer do not remain, no problem occurs. This is because the fragments of the black layer that intrude into the interior surface during the step of trimming of the black layer can be completely removed in the course of following steps of dissolving and peeling of the resist layer or the like.
The objects of the present invention are to provide a color cathode ray tube that can prevent fragments of black layer, which occur in trimming an optical filter layer, from adhering and remaining on an interior surface of a panel to give a defect-less display, and to provide a method for manufacturing such color cathode ray tubes with high yield.
A first aspect of the present invention is a color cathode ray tube, the color cathode ray tube comprising a transparent panel, a funnel joined airtightly to a circumference portion of a sidewall of the panel, a light absorption layer and an optical filter layer disposed on an interior surface of the panel, and a phosphor layer formed on the optical filter layer. Here, a length from an edge of the panel joined to the funnel to a circumference edge of the light absorption layer formed on an interior surface of the sidewall of the panel is longer than or equal to the length from the edge of the panel joined to the funnel to a circumference edge of the optical filter layer formed on the interior surface of the sidewall of the panel.
A second aspect of the present invention is a manufacturing method of a color cathode ray tube, the method for manufacturing the color cathode ray tube comprising the steps of forming a light absorption layer on an interior surface of a transparent panel, forming an optical filter on an interior surface of the panel on which the light absorption layer is formed, forming a phosphor layer (71R, 71G, 71B) of each color on the corresponding optical filter layer (72R, 72G, 72R) with an arrangement of a prescribed pattern, and joining a funnel airtightly to a circumference portion of the sidewall of the panel (FIG. 7). Here, the step of forming the light absorption layer comprises the steps of forming a resist layer of a prescribed pattern on the interior surface of the panel; of coating on the resulting structure a dispersion liquid of light absorption material to be fixed on the resulting structure; of scraping and removing surplus light absorption layer adhered on an interior surface of the sidewall of the panel as a trimming; and of dissolving the resist layer to be peeled off and removed together with the light absorption layer formed thereon. Here, the step of forming the optical filter layer comprises the steps of forming a filter layer of a plurality of colors with a prescribed pattern on the interior surface of the panel; and of scraping and removing the surplus filter layer adhered on the interior surface of the sidewall of the panel as a trimming. Here, a length from an edge of the panel being joined to the funnel to a scraping edge of the light absorption layer in the trimming step of the light absorption layer is longer than or equal to a length from the edge of the panel to a scraping edge of the filter layer in the trimming step of the filter layer.
In the following, the present invention will be described in more detail.
In a color cathode ray tube of the present invention, as shown in FIG. 1, a length (a) from a joined edge 2 with a funnel (not shown in the figure) of a panel 1 to a circumference edge of a light absorption layer (black layer) 3 adhered and formed on an interior surface of a sidewall 1s of the panel 1 is longer than or equal to a similar length (b) of an optical filter layer 4 (axe2x89xa6b). A black layer 3 and a filter layer 4 constituted with such a structure can result in the following way. That is, in the trimming step of the surplus black layer 3 adhered onto the interior surface of the sidewall 1s of the panel 1, a length (trimming dimension) (a) from the edge 2 of the panel to a scraping edge of a black layer 3 is made longer than or equal with a trimming dimension (b) of a filter layer 4 in the trimming step of the surplus filter layer 4.
When constituted with such a structure, in the trimming step of the filter layer 4, the black layer 3 is not further scraped. Accordingly, fragments of the black layer 3 do not enter into and remain on the interior surface of the panel 1 (faceplate) thereby resulting in a color cathode ray tube of excellent image quality with no display defects. In addition to this, there is no need to increase the degree of water washing more than normal, and thus deterioration of yield due to peeling off of the filter layer 4 can be prevented from occurring.
In addition, in the present invention, by the following reasons, it is more desirable to make the trimming dimension (a) of the black layer 3 longer (a greater than b) than that (b) of the filter layer 4 rather than equalizing (a=b) them so that the upper filter layer 4 completely covers the circumference portion of the lower black layer 3. That is, in trimming, there are limits of accuracy in setting the panel 1 on a carrier and in disposing a device for trimming. Accordingly, it is difficult to set the trimming dimension of the panel 1 accurately to be equal over the entire circumference of the panel 1. When the trimming dimension of the black layer 3 and that of the filter layer 4 are set equal (a=b), there may still be portions of the lower black layer 3 that are not covered by the upper filter layer 4. In trimming the filter layer 4, the circumference edge of the black layer 3 may be partly trimmed again. Accordingly, in order to completely prevent the fragments of the black layer from entering and remaining on the interior surface of the panel, taking safety factors into consideration, it is desirable to set a greater than b.
In the present invention, in trimming the black layer or filter layer, scraping with a rotary brush or immersing in liquid of decomposing agent such as an aqueous solution of ammonium fluoride is implemented. In scraping by use of a rotary brush, from durability of the brush or accuracy of the device, the scraped edge portion may become wavy, that is, an identical trimming dimension cannot be obtained over the entire circumference. Further, in trimming the filter layer, the lower black layer may be scraped due to the rotary brush. Accordingly, it is desirable for the trimming to use immersing in an aqueous solution of decomposition agent such as ammonium fluoride to dissolve and peel the surplus black layer and the filter layer, followed by washing with water.